Mercury concentrations in cephalopods from the Pacific sector of the Southern Ocean in relation to their biology, habitat and trophic position

Mercury (Hg) can negatively affect marine biota through uptake from prey and from the surrounding environment. Cephalopods constitute a major prey group in Southern Ocean ecosystems, yet little is known about Hg concentrations in these taxa and how biological and ecological factors can influence Hg body burdens. By combining stable isotope analyses (δ13C and δ15N) and Hg concentrations in beaks from 25 cephalopod species from the Pacific sector of the Southern Ocean, we studied 1) habitats and trophic positions; 2) Hg concentrations; and 3) how Hg concentrations relates to lower rostral length, habitat and trophic position of the studied species. Our results showed that δ13C values indicated that species inhabited various water masses, with Alluroteuthis antarcticus inhabiting further north than previously reported. Additionally, δ15N values of these cephalopod species showed that cephalopods in the Pacific sector of the Southern Ocean occupy two to three trophic levels with Hg concentrations among studied cephalopod species increasing from southern to northern habitats. Mercury concentrations in cephalopod beaks ranged from 0.003 μg g−1 (Filippovia knipovitchi) to the highest concentration ever recorded in cephalopod beaks (0.590 μg g−1 in Histioteuthis atlantica), with Hg concentrations increasing with the lower rostral length in H. atlantica but decreasing in Moroteuthopsis ingens. Our results suggest that Hg concentrations in Southern Ocean cephalopods may be driven by species-specific factors rather than a general pattern across species. This study emphasizes the need for cephalopod species-specific research on Hg bioaccumulation and biomagnification to better understand its impact on Southern Ocean marine food webs.